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From: Hekuang <hekuang@huawei.com>
Subject: [BUG ARM64/perf] Perf record on hardware breakpoint causes
 application to hang
Message-ID: <56D83771.2090101@huawei.com>
Date: Thu, 3 Mar 2016 21:09:05 +0800
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This problem can be reproduced as follows:

We know cat /proc/version will read the memory of symbol
linux_proc_banner, then we make a hardware memory access
breakpoint on that address.

on terminal 1:

   $ perf record -e mem:0x$(cat /proc/kallsyms|grep 
linux_proc_banner|cut -d " " -f 1):rw --no-buffer -a

on terminal 2:

   $ cat /proc/version

Then our 'cat' process on terminal 2 will be hanged, until we press
'^C' to stop perf from recording events.

The sample numbers recorded by perf is extraordinary too:

   [ perf record: Captured and wrote 0.879 MB perf.data (22691 samples) ]

The right result can be produced by removing the 'no-buffer'
argument in perf command line, and the result should be like
this:

   $ perf record -e mem:0x$(cat /proc/kallsyms|grep linux_proc_
                            banner|cut -d " " -f 1):rw  -a
   ^C
   [ perf record: Woken up 1 times to write data ]
   [ perf record: Captured and wrote 0.013 MB perf.data (10 samples) ]

Report this bug to you and hope for answers.

Thanks.